Phased array ultrasonic testing (PAUT) is presented in detail in the American Welding Society (AWS) D1.5 Bridge Welding Code (BWC). The code book presents the usual sections including Scope, Definitions, Personnel Requirements, Equipment, etc. In this article, the focus is on phased array ultrasonic testing (PAUT) accept/reject criteria and how to apply them real data from a structural steel welds.
AWS Bridge Welding Code PAUT Acceptance Criteria
The BWC defines four different discontinuity classes: A, B, C, and D. Discontinuity Class A is the most severe, intermediate Classes B and C, and least severe Class D. They are categorized by the ultrasonic wave reflected amplitude of the weld discontinuity detected by phased array. The four different amplitude threshold levels are Automatic Reject Level (ARL), Standard Sensitivity Level (SSL), and Disregard Level (DRL). The SSL is set using the 0.060” diameter side drilled hole (SDH) on the IIW calibration block to 50% full-screen height (%FSH). The ARL is set 5 dB above the SSL and which is equivalent to 89 %FSH. Lastly, the DRL is set to 25 % FSH. The phased array discontinuity classes are defined in the AWS D1.5 Discontinuity Classification table shown below.
In addition to ultrasonic testing discontinuity classification, the BWC also defines PAUT minimum discontinuity lengths by types of by discontinuity classification. The allowable lengths are further classified by type of loading: compression and tension. For compression connections, the maximum lengths for Classes A, B, and C are non-allowed, 20 mm, and 50 mm, respectively. For tension joints, the maximum lengths for Classes A, B, and C are non-allowed, 12 mm, and 50 mm (middle) and 20 mm (top and bottom quarters), respectively. These criteria are outlined in the PAUT Acceptance Criteria outlined below.
In addition to the rules outlined in the PAUT Discontinuity Classification and Acceptance Criteria tables, there are some additional discontinuity separation criteria that must also be considered. Classes B and C reflections must be separated by at least 2 times the length of the longer indication. Additionally, Class B and C indications must not initiate at a distance less than 2 times the length from the weld end.
Example Phased Array Ultrasonic Testing Setup and Data
Figure 1 shows example data from a 1” thick steel plate with a single-vee joint and backing bar. The standard sensitivity level was set to 50 % FSH using the 0.060” side drilled hole on the IIW block. On the Olympus MX-2 platform, this step is accomplished during the sensitivity calibration step. During this step, compensation gain is added to each focal law that accommodates the attenuation characteristics of each phased array focal law or beam. In addition, a secondary sizing calibration step was performed to establish a TCG/DAC function that normalizes the amplitude response from the 0.060 side drilled hole over the desired testing range. Typically, a NAVSEA or comparable block, is used for this step.